The present invention relates generally to a switch matrix particularly suited for satellite communication applications and more particularly, to an apparatus and method for minimizing the quantity of interconnected switches within the switch matrix.
Various systems exist that require a large number of multi-channel configurations in which many inputs are interconnected to many outputs such as in communication systems. To satisfy this need, switching networks have been developed containing tens to thousands of interconnected switches. These switching networks include decomposing or partitioning a variable number of inputs (N) to a variable number of outputs (M). An example of this is a telephone communication network that uses non-blocking switch matrices, which allow any combination of N inputs to be connected to M outputs. A non-blocking switch is defined as one where any combination of M of N inputs can be connected to the M outputs and existing connections within the switch matrix need not be modified when a new connection is made.
A direct measure of the complexity of a switch matrix is the number of interconnecting switches required to implement the switching. In satellite communication systems and other communication systems, there is a continuing effort to decrease the quantity of the switches in a switch matrix while increasing the degree of signal isolation and redundancy of the switch matrix.
Weight is a concern for satellite communication systems. Satellite communication systems using switch matrices may be very heavy, and the weight is directly related to the size of the switch matrix. For example a switch matrix having 784 inputs and 784 outputs can weigh approximately 1000 lbs. Another reason for reducing the interconnecting switch count is to reduce the amount of hardware, electronics, power splitters, and switches within a communication system thereby lowering costs and reducing weight.
The degree of isolation in a switch matrix is related to the level of unwanted interference on a desired output signal from other disjoint inputs. In large switch matrices, the large number of disjoint signals, can cause an unacceptable amount of interference on a given signal. Each additional switch per signal path increases the isolation of the signals within a system. For example, an increase of interconnecting a single switch in a signal path increases the level of isolation by 20-40 db at microwave frequencies. Therefore, an increase in the number of switches may be desirable to improve isolation, but the corresponding increase in size and weight may be unacceptable.
Redundancy of the switch matrix corresponds to the versatility and ability, in case of a failure, to reroute a signal around the failing component. Hence, more potential signal paths for rerouting are desirable to circumvent failures. A measure of redundancy is the number of available paths K for a given number of required paths Kxe2x80x2. The redundancy is stated as K for Kxe2x80x2, which means that K-Kxe2x80x2+1 paths from the K paths must fail before the switch matrix is unable to route the signals. Therefore, increasing the redundancy within a switch matrix increases the reliability of the communication system. Unfortunately, improvement in redundancy corresponds to an increase in the total switch count within a switch matrix. The ability to improve the redundancy in a switch matrix by increasing K in small increments is an important advantage since the complexity as well as the reliability increases as K increases. Thus, the ability to increase K by small amounts can improve reliability while not increasing complexity.
One solution, which is fundamental to other methods in the art, is a non-blocking crossbar network. The non-blocking crossbar network has two approaches shown in FIGS. 1A and 1B. The first approach has a single pole single throw (SPST) switch at each interconnection. The second approach has two SPST switches at each interconnection.
Referring now to FIG. 1A, a conventional crossbar switch matrix having a SPST switch at each connection is shown. N input ports 1 are connected to N input circuits 2 containing 1:M power splitters 3 and M interconnect switches 4. One interconnect switch 4 of each of the N input circuits 2 is connected to the N inputs of an output circuit 5. Each of the M output circuits 5 consist of an N:1 power combiner 6.
Referring now also to FIG. 1B, a conventional crossbar switch matrix having two SPST switches per connection is shown. Each of the M output circuits 5 consists of an N: 1 power combiner 6 plus N switches 7.
In both approaches, M of the N input signals is routed to the M output ports 8. The first approach has Nxc3x97M SPST interconnected switches 9. The second approach has 2xc3x97Nxc3x97M SPST switches 9. Although the second approach has twice the number of interconnected switches 9, it also has twice the degree of isolation between unused connections and the desired signal. The non-blocking simple crossbar switching network is applicable for broadcast mode in which a given input can be connected to any number of outputs, and non-broadcast mode in which at most one output is connected to a given input. The power splitters 3 and combiners 6 allow the same input signal (or port) 1 to be routed to multiple output ports 8. At low frequencies, the power splitters are not needed for broadcast mode.
A disadvantage of the non-blocking crossbar-switching network is that it contains the highest number of interconnected switches of existing methods known in the art. Furthermore, adding two switches in parallel doubles the complexity of the switch matrix.
Another solution decomposes an Nxc3x97M switch matrix into three or more stages of interconnected smaller crossbar switch modules. As used herein, decomposition refers to a collection of signals that is partitioned and distributed among multiple switches that are interconnected. The architecture in this solution is intended for interconnected switches in which the connection of an input to a particular output is important. For networks having the same number of outputs (M) as inputs (N) and an optimum number of output modules (P), the switch count is approximately 4xc3x9721/2xc3x97N3/2xe2x88x924xc3x97N. The architecture of this solution has the isolation of two switches per connection when used with one switch per connection crossbar modules. Although K for Kxe2x80x2 redundancy can be achieved in small increments, a disadvantage with this architecture is that it consists of three or more stages of interconnected switches and, therefore, a large number of switches.
Yet another solution utilizes binary decimations and full broadcast. These binary architectures require 4N(log2(N)xe2x88x921)+4M SPST switches using two switches per connection. One disadvantage with binary architectures is the use of 2xc3x972 crossover switch modules, which have limited isolation because of the crossover geometry in high frequency applications. Another disadvantage is that this architecture requires doubling the switch count, to provide a preferred amount of redundancy capability.
Therefore, a need exists to reduce the size and weight of the switch matrix. Significantly decreasing the weight of a satellite communication system has the potential of saving millions of dollars in production and implementing costs.
Although a need exists to reduce the size and weight of a communication system an opposing need exists to increase the degree of isolation.
Additionally, in communication systems, a need exists to increase the number of signal paths in the switch matrix thereby increasing the redundancy capability and reliability of the communication system.
The present invention has several advantages over existing microwave switch matrix architectures. The present invention significantly decreases the number of interconnected switches required in a switch matrix over the prior art while at the same time maintaining the required number of signal paths for a particular application in which the connection of an input to a particular output is not important. The present invention, although decreasing the number of interconnected switches, also provides for increased degree of isolation and redundancy capability between signal paths within the switch matrix.
The forgoing and other advantages are provided by a switch matrix comprising a plurality of first input interconnections N, a plurality of second output interconnections M, a plurality of input modules X, and a plurality of output modules P. Each input module has a group of input interconnections selected from the plurality of first input interconnections, a plurality of first interconnected switches, and a plurality of first output interconnections. Each output module has a plurality of second input interconnections, a plurality of second interconnected switches, and a group of output interconnections selected from the plurality of second output interconnections. The plurality of first output interconnections is electrically coupled to the plurality of second input interconnections. The plurality of input modules X are electrically coupled to the plurality of output modules P, to form a plurality of signal paths having a plurality of interconnected switches K per signal path.
Additionally, a method for minimizing the number of interconnected switches Z is also provided. The method comprises determining the values of X and P and performing an integer partitioning process.
The present invention itself, together with further objects and attendant advantages, is best understood by reference to the following detailed description, with reference to the accompanying drawings.